Comment by fapjacks

No, it is not feasible to run modem signals over VOIP, as the various codecs all compress signals and cut frequencies and all manner of things to reduce bandwidth consumption, which are incompatible with modem signaling. You could get away with it in a homelab for fun, but you have absolutely no control over what VOIP codecs e.g. Comcast is running, so it is effectively impossible. Even if the phone company says they can offer you a copper line, your copper line will eventually get converted to VOIP at the end of the street or wherever, and then it's up to whatever commercial provider you're paying to choose the codecs for VOIP, which are never modem-friendly. I worked on this stuff about ten years ago. There are fax codecs but they are very hard to get working reliably.